A new study by MIT researchers reveals that despite regional variability in climate, electricity sources, congestion, and individual driving patterns, electric vehicles (EVs) generate less greenhouse gas emissions and do not cost more than comparable gas-powered vehicles for drivers and vehicle fleet owners in most parts of the United States. The team’s approach captures many key factors contributing to regional and individual differences in the life-cycle emissions and ownership costs of EVs, including meteorological data, trip distances and durations, and fuel prices. To provide a more comprehensive picture of emissions and costs, researchers sourced data from thousands of U.S. zip codes and drilled down to the level of individual drivers within those locations, considering time-averaged fuel prices to mitigate the influence of price fluctuations. Their analysis indicates that driving behaviors can be as significant as regional factors like local electricity mix regarding emissions savings from EVs compared to similar gas-powered vehicles. In most locations, battery-electric vehicles reduce emissions by 40% to 60%, with larger impacts in urban areas. The study also found that colder climates do not diminish overall emission benefits as much as some media claims suggest. The researchers updated a public tool, carboncounter.com, which allows users to compare life-cycle emissions and total ownership costs of nearly any car on the market, with a new version also being released today. Marco Miotti, PhD ’20, a senior researcher at ETH Zurich and a former MIT graduate student, stated, “Many claims suggest that electric vehicles don’t reduce emissions significantly in cooler climates, and we aimed to systematically analyze these factors and evaluate these claims simultaneously. Rather than simply asking, ‘Are EVs better?’, this paper helps answer ‘better for whom, and under what conditions?’”
Many prior studies comparing emissions and costs of EVs to internal combustion vehicles cover a limited number of factors, such as the amount of renewable energy in the grid and how gas prices impact affordability. Miotti notes, “To our knowledge, there have been few efforts so far that bring all these factors together. But if someone wants to buy a car and understand the factors affecting emissions and costs, this holistic approach is important.” The researchers focused on two types of EVs: battery-electric vehicles, which operate solely on electricity, and plug-in hybrid electric vehicles, which combine a combustion engine with a battery to optimize fuel savings. They expanded and improved a set of previously developed vehicle cost and emissions models to incorporate a wider variety of factors and data types. For instance, they refined an existing model estimating energy use and gas mileage to capture more nuances of local climate variability.
The team sourced data on various factors for each U.S. zip code, such as typical drive cycles, traffic levels, local gas and electricity prices, regional electricity mix, meteorological profiles, and more. They utilized statistical approaches to amalgamate different types of data. For example, they employed a probabilistic matching technique to combine nationwide travel survey data on driving frequency with more detailed GPS data, which includes drivers’ acceleration patterns and typical daily driving distances. The analysis was designed to focus on the spatial picture of emissions and costs based on U.S. zip codes, while also considering the size and features of each specific vehicle model.
Ultimately, their modeling framework revealed that all factors analyzed matter equally in determining the emissions reduction potential of EVs compared to internal combustion vehicles. EVs reduce emissions most in areas with cleaner electricity mixes, denser traffic, higher annual travel distances, and mild climates, in decreasing order of importance. In each area, emission reductions increase for drivers who drive more often, drive larger vehicles, and experience more traffic congestion. In colder areas like North Dakota, the fuel economy of battery-electric vehicles may drop by as much as 50% on particularly frigid nights, but the effect on annual emission benefits is minimal. “We even conducted a sensitivity study to see if range is reduced in very cold climates, and we found that, even in the most unfavorable conditions, EVs still reduce emissions significantly,” says Miotti.
On the cost side, the models show that in most parts of the U.S., EVs are competitive with comparable combustion-engine vehicles in terms of lifetime ownership costs, even without clean vehicle tax credits. In areas where electricity is relatively affordable, battery-electric vehicles tend to cost less than their plug-in hybrid or combustion-engine counterparts. In the future, the researchers aim to expand this analysis to include a temporal dimension, considering how changes in vehicle, fuel, and electricity prices affect emissions and costs over time. Miotti concludes, “While we found that the electricity mix is a big driver of the spatial variation in emissions savings of EVs, the electricity grid is decarbonizing everywhere. As that happens, emissions savings across space will become more homogenous for EVs, but the differences across individual drivers will remain.” This work was partially funded by the MIT Martin Family Society of Fellows for Sustainability.
Blogger's Review: This MIT study underscores the critical intersection of technology and environmental science, revealing that EVs can be both cost-effective and environmentally friendly across diverse U.S. regions. The nuanced analysis presented highlights the importance of understanding individual driving behaviors and local conditions, making it essential for informed decision-making in the transition to sustainable transportation.